This application claims the priority of German patent 197 47 270, filed Oct. 25, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a motor vehicle having an automatic transmission and to a process for shifting such an automatic transmission.
Automatic transmissions within the scope of the invention are fully automatic transmissions, in which gears are shifted automatically as a function of the driving speed as well as partially automatic transmissions, in which a driver can manually select the gear speeds and the selected gear is then shifted automatically, as well as transmissions which comprise both possibilities.
In most motor vehicles, the engines and the transmission remain in the same adjustment in all operating situations, particularly the advance angle in the case of Otto engines and the system fluid pressure for operating shifting clutches and shifting brakes in the automatic transmission. The engine reacts only to changes of the position of the gas pedal. In the following, instead of "gas pedal", the term "driving element" will be used for all types of foot-operable or manually operable fuel adjusting elements of Otto engines and of diesel engines.
In practice, it is known, at least in the case of higher-priced vehicles, to change, during a change-speed operation of the automatic transmission, the advance angle of an Otto engine or to throttle the diesel fuel injection of a diesel engine or to lower the system pressure of the fluid which operates shifting clutches and/or shifting brakes, so that the gears are shifted "smoothly", particularly when the motor vehicle is rolling, for example, downhill, while the engine power is set to a low value at the driving element, or during a "slow" acceleration.
The invention relates to automatic transmissions in which, during a speed change, the combination of the gear wheels which mesh with one another is changed. For this purpose, the automatic transmission contains shifting clutches and usually also shifting brakes. For simplifying the description, only the term "shifting clutches" will be used which also includes shifting brakes.
Basically, in the case of all known motor vehicles, a "critical shifting condition" will occur when one or several shifting clutches of the automatic transmission are pushed into their closing position not by means of the complete fluid system pressure. Such a critical shifting condition will exist:
a) When a connected (output) shifting clutch of the previous gear and a connected (input) shifting clutch of the new gear are both operating with a slip in the frictional operation; that is, when both shifting clutches are in the delivery phase. In this delivery phase, the engine may have an undesirably high rotation or may overrev if the driver suddenly sets a significantly higher engine power at the driving element. PA1 b) When the connected shifting clutch is just before the synchronous operation with the transmission part (gear wheel or a planet carrier of a planetary transmission), and the disconnected shifting clutch is already fully open; or when the connected shifting clutch has reached the synchronous operation with its transmission part but its clutch closing pressure has not yet risen to the full system pressure. During these two shifting phases, torque jolts, for example, as the result of a significantly higher engine output suddenly set by the driver at the driving element, are undesirable because they may cause the connected shifting clutch to slip more or to slip again before it will then be completely closed when the full system pressure of its clutch fluid is reached. PA1 c) When the fluid pressure of the disconnected shifting clutch was lowered to below the full system pressure by an initiated shifting operation and holds the disconnected shifting clutch just barely still completely closed or still in the friction slip operation.
This means that the "critical shifting condition" starts as soon as the fluid closing pressure of a disconnected shifting clutch falls below the full system pressure, the critical shifting condition then continuing in the delivery phase, and then still lasting until the connected shifting clutch of a newly selected gear is displaced by its operating fluid so far into the closing position that it can no longer slip at the engine power set by the driver at the driving element.
The driving element can be mechanically connected by means of a linkage or a cable control with the fuel feeding device of the engine, such as a carburetor or an injection system, or can be coupled electronically. The currently known electronic fuel adjusting systems in motor vehicles act like the conventional mechanical fuel adjusting systems. In this case, a power change of the engine desired by the driver of the motor vehicle, and thus a torque change, when the driving element is operated, immediately results in a corresponding increase or reduction of the engine power and of its torque. If the driver suddenly desires a significant power change and sets it at the driving element, while a shifting operation is taking place in the automatic transmission, the considerable rise of the engine torque may lead to a poor shifting comfort. For example, automatic gear shifts during the coasting of the vehicle are particularly critical, or the shifting of gears while the engine is running with little gas or standing gas and, in this case, shifting clutches are operated at very low clutch pressures for optimizing the shifting comfort. If, during such a condition, the driver suddenly significantly increases the torque of the engine at the driving element so that a fast rise of the torque occurs at the engine, the fluid pressure control, which controls the pressure of the operating fluid of the shifting clutches of the transmission, may not sufficiently rapidly follow the fast torque rise of the engine so that a considerable slip will occur in the shifting clutches and the engine will rev, before the operating fluid of the shifting clutches reaches to full system pressure and closes the shifting clutches again. This results in a significant shifting jolt.
It is an object of the invention to significantly improve, in the case of motor vehicles with a partially automatic or fully automatic transmission and an electronic fuel adjusting system, the shifting comfort during critical shifting phases of the automatic transmission.
This and other objects have been achieved according to the present invention by providing a process for shifting an automatic transmission in a motor vehicle having an internal-combustion engine and an electronic engine timing system which is electrically coupled with a driving element, the driving element being adjustable by a driver to demand a change in output of the engine, the automatic transmission having an electronic transmission control system which automatically shifts transmission gears, wherein the electronic transmission control system is electrically coupled with the electronic engine timing system and both of said systems are constructed such that when (a) an adjustment of the driving element is being made to demand an increase in the output of the engine to a desired higher output, and simultaneously (b) a gear shift operation is taking place in the automatic transmission and the automatic transmission is in a critical shifting phase in which an undesirable slip operation condition or an undesirable jolt-type termination of a slip operation would occur if the engine output were immediately increased to said desired higher output, then, the increase in output from the engine is controlled according to at least one of the following conditions: (i) delaying the increase in output from the engine for a period of time; and (ii) reducing or limiting a gradient of the increase in output from the engine via the engine timing system.
This and other objects have been achieved according to the present invention by providing a motor vehicle having an automatic transmission, an internal-combustion engine, and an electronic engine timing system which is electrically coupled with a driving element, the driving element being adjustable by a driver to demand a change in output of the engine, the automatic transmission having an electronic transmission control system which automatically shifts transmission gears, wherein the electronic transmission control system is electrically coupled with the electronic engine timing system and both of said systems are constructed such that when (a) an adjustment of the driving element is made to demand an increase in the output of the engine to a desired higher output, and simultaneously (b) a gear shift operation is taking place in the automatic transmission and the automatic transmission is in a critical shifting phase in which an undesirable slip operation condition or an undesirable jolt-type termination of a slip operation would occur if the engine output were immediately increased to said desired higher output, if a rate of the adjustment and an extent of the desired higher output each exceed respective predetermined values, the increase in output from the engine is controlled according to at least one of the following conditions: (i) the increase in output from the engine is delayed for a period of time; and (ii) a gradient of the increase in output from the engine is reduced or limited by the engine timing system.
This and other objects have been achieved according to the present invention by providing a method of controlling a transmission with automatically shiftable gears in a motor vehicle having an internal-combustion engine, said method comprising the act of: when a demand for increased engine output is made while the transmission is in a critical shifting phase of a gear shift operation, controlling an increase in the engine output according to at least one of the following conditions: (i) delaying the increase in the engine output for a period of time; and (ii) reducing or limiting a gradient of the increase in engine output.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.